In seismic exploration, seismic data are acquired by imparting acoustic energy into the earth near its surface, and detecting acoustic energy that is reflected from boundaries between different layers of subsurface earth formations. Acoustic energy is reflected when there is a difference in acoustic impedance between layers disposed on opposite sides of a boundary. Signals representing the detected acoustic energy are interpreted to infer structures of and composition of the subsurface earth structures.
In marine seismic exploration, (seismic exploration conducted in a body of water) a seismic energy source, such as an air gun, or air gun array, is typically used to impart the acoustic energy into the earth. The air gun or air gun array is actuated at a selected depth in the water, typically while the air gun or air gun array is towed by a seismic survey vessel. The same or a different seismic survey vessel also tows one or more seismic sensor cables, called “streamers”, in the water. Generally the streamer extends behind the vessel along the direction in which the streamer is towed. Typically, a streamer includes a plurality of pressure sensors, usually hydrophones, disposed on the cable at spaced apart, known positions along the cable. Hydrophones are sensors that generate an optical or electrical signal corresponding to the pressure of the water or the time gradient (dp/dt) of the pressure in the water. The vessel that tows the one or more streamers typically includes recording equipment to make a record, indexed with respect to time, of the signals generated by the hydrophones in response to the detected acoustic energy. The record of signals is processed, as previously explained, to infer structures of and compositions of the earth formations below the locations at which the seismic survey is performed. The invention described herein is an improved method for processing data, and more specifically an improved method for depth migration of seismic data.
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the scope of the present invention as defined by the appended claims.